The underground station was opened on July 17, 1918, as Mott Haven Avenue station as a southbound extension of the Jerome Avenue Line into the Upper East Side extension of the IRT Lexington Avenue Line. As such, it is the newest station on the line. The segment north of Kingsbridge Road to Woodlawn opened three months earlier.[4] It has two side platforms and three tracks, and is the only other station on the line to be built underground. The center express track is used by the 4 train during rush hours in the peak direction.

Both platform walls have their original mosaic trim line with "MH" tablets on it, a relic of the former name Mott Haven Avenue. The original name tablets are covered with black plates reading "138 Street" in white Akzidenz-Grotesk lettering. At either ends of the platform, where they were extended in the 1950s, the walls have a blue trim with "138TH ST" in white lettering. Blue i-beam columns run along both platforms at regular intervals with alternating ones having the standard black number plates in white lettering. Until 1972, it had a connection to the 138th Street Station which served both the Harlem and Hudson Divisions of the New York Central Railroad.[5][6]

In 2011, the advocacy group Transportation Alternatives took a poll of subway riders to "rank the stank" (i.e. vote for the smelliest subway station in the system). This station was ranked the smelliest of four nominated stations, receiving 35% of the votes.[7]

This station has one mezzanine above the center of the platforms and tracks. Two staircases from each platform go up to a waiting area/crossover, where a turnstile bank provides access to and from the station. Outside fare control, there is a token booth and two staircases going up to either northern corners of East 138th Street and the Grand Concourse. The mezzanine has its original "Uptown Trains" and "Downtown Trains" mosaic tablets and trim line.[8]